Diffusion in concentrated micellar and hard sphere solutions

S. Walrand , L. Belloni , M. Drifford

We present experimental results of quasi-elastic light scattering for different charged micellar solutions. The characteristic concentration dependence of the mutual diffusion coefficient Dm at large volume fraction arises from the many-body hydrodynamic interactions. These interactions are introduced through the quasi-empirical screened Navier-Stokes equation. The effective pair mobility tensor has been calculated for terms up to r -7 (r is the inter-particle distance) with the formalism of Mazur and van Saarloos. The tensor is not « screened » in the sense that its long distance behaviour is as an inverse power of r, rather than exponential. A single « screening » constant K is proposed which is volume fraction dependent with only one adjustable parameter. The evolution of Dm with the micellar concentration has been well reproduced by the same value of K at various ionic strengths. At large volume fraction Φ the hydrodynamic interactions are essentially dominated by uncharged hard-sphere repulsions. This observation is confirmed by the fit of the dynamics of concentrated hard-sphere solutions. The behaviour of the self and mutual diffusion coefficients is described by using the same « screening » constant. This can be written as Ka ≃ Φ where a is the particle radius, which is in agreement with the results previously derived by Adelman.

Mots clés: colloids; diffusion in liquids; light scattering

Domaines: Articles anciens

S. Walrand, L. Belloni, M. Drifford. Diffusion in concentrated micellar and hard sphere solutions. Journal de Physique, 1986, 47 (9), pp.1565-1576. ⟨10.1051/jphys:019860047090156500⟩. ⟨jpa-00210356⟩